The present invention relates to pressure sensors. More specifically, the invention relates to pressure sensors which measure deflection using optical techniques.
Pressure sensors are used to measure pressures of various media and have a wide range of uses in industrial, commercial and consumer applications. For example, in industrial process control, a pressure sensor can be used to measure the pressure of a process fluid. The pressure measurement can then be used as an input to a formula which provides an indication of another process variable such as a fluid level or a flow rate.
There are a number of different techniques which are used to measure pressures. One basic technique involves the use of a deflectable diaphragm. In such a pressure sensor, a pressure is applied to the diaphragm, either directly or through an isolating medium, and the deflection of the diaphragm is measured. Various deflection measurement techniques can be used. For example, a strain gauge mounted to the diaphragm can provide an indication of deflection. In another technique, the deflection causes a change in capacitance which can be measured and correlated to the applied pressure. Preferably, pressure sensors are able to have long lives, provide high accuracy and are capable of withstanding environmental extremes, exposure to caustic fluids, vibrations, impacts and other potentially damaging inputs.
Typically, the techniques which are used to measure deflection require electrical contact to electrical components which are carried on the pressure sensor. Such contact can be difficult to achieve and can be a source of failure. Additionally, the additional processing as well as the electrical components themselves can be a source of errors in pressure measurements.
In one aspect, the present invention provides a pressure sensor which does not require electrical contact to the diaphragm of the sensor or the surrounding material.
The pressure sensor is configured to sense an applied pressure. A diaphragm support structure is coupled to a diaphragm which deflects in response to applied pressure. A moveable member is coupled to the diaphragm and moves in response to deflection of the diaphragm. An optical interference element moves with the moveable member and is configured to interfere with incident light. The interference is a function of position of the moveable member. In one aspect, the moveable member is coupled between opposed diaphragms. In this configuration, a pressure sensor is less susceptible to being damaged when exposed to high pressures.